The family record, which was written by Stevenson’s grandfather, Robert, details births, deaths and marriages in the family over many generations.
Stevenson's family bible, which has been donated, contains marks and notations throughout, from years of heavy use.
Curator Anna MacQuarrie said: "Our Stevenson collections speak to the life and experiences of this great writer, both as a young boy and his later days spent in the South Seas.
"These new donations are a wonderful addition to the collection, allowing us to imagine what kind of influence these objects might have had on his young life and later inspirations.
"We are sincerely grateful to the donor for their generosity, enabling the wider public to better understand Stevenson and his family background”.
The donor of the items said: “I was touched by the gracious, enthusiastic attitude of the curators to whom I recently passed on family items, pertining to Louis/RLS and the lighthouse engineer side of our family.
"Gifting was made easier by the knowledge and assurance that a wider public would benefit from being able to see other pieces in the familial, Stevenson jigsaw puzzle. It was a relief to realise that the items would be honoured and cared for - and subsequently appreciated by many other interested parties”.
Jeremy Hodges, Robert Louis Stevenson biographer and co-ordinator of the annual RLS Day celebrations, said: "Despite the international fame of RLS as an author, he always felt slightly guilty about not following in his father’s footsteps as a builder of lighthouses – a proper job of more importance than making stories.
"He remedied this in part by writing Records of a Family of Engineers, drawing on the kind of genealogical material that forms part of this bequest.
"The family Bible would have been treasured by the devout Robert Stevenson and his descendants, including Robert Louis – despite his announcement in his early twenties that he no longer believed in the Christian religion, a confession that led to traumatic rows with his God-fearing parents”.